1. Field of the Invention
This invention relates to a tracking system and tracking method. More particularly, but not exclusively, it relates to a tracking system and method that is operable upon an unauthorised movement of an object, for example a motor vehicle.
2. Description of the Related Art
The tracking of stolen motor vehicles is well known and techniques for doing so range from the concept of an alarm sounding from which a vehicle can be audibly tracked to the use of the Global Positioning System (GPS) to track vehicles once they are known to be stolen.
An audible alarm is primarily a deterrent with notification of the presence of the alarm being intended to be sufficient to ward off casual or petty thieves. However, determined or professional car thieves will typically be able to disable most audible alarms either before stealing the vehicle, by use of infrared code scanners, or manually within seconds of effecting entry to the vehicle, thus giving the impression of a fake alarm or an accidental actuation of the alarm by the vehicle's owner.
GPS tracking systems suffer from the problem that it is necessary to have three satellites within a line of sight of the vehicle in order to be able to accurately determine the position of the vehicle. This is not always possible in the urban environment, particularly in cities, due to the surrounding buildings. This can lead to the inaccurate determination of the location of the stolen vehicle, or an imprecise location.
Another drawback of GPS tracking systems is that the owner must know that the vehicle has been stolen prior to the system being activated. This can give the thief a significant amount of time to get away and even cross jurisdictional boundaries.
WO 95/22131 discloses a tracking device in which signal strengths and identification information from cellular transmitters received at the device are retransmitted to a remote monitoring station along with information relating to the direction and distances travelled by the vehicle. A computer at the remote monitoring station determines the position of a vehicle using the information transmitted from the device. The direction and distance information is typically used when the vehicle cannot receive adequate signals from the cellular transmitters to triangulate.
U.S. Pat. No. 5,767,804 and U.S. Pat. No. 6,094,164 disclose a tracking system using radio direction finding and a GPS receiver.
WO 98/01769 discloses a tracking system using a GPS receiver and a gyroscope.
U.S. Pat. No. 6,327,219 discloses a system for directing a following device toward a moveable object using radio frequencies and an ultrasonic signal.
GB 2360588 discloses a navigation system for directing a user to a destination using GPS.